The present invention relates to a discharge lamp, a light source apparatus which prepares illumination rays using the discharge lamp, and a projection display apparatus which projects a large image onto a screen using the light source apparatus, a spatial light modulating element (for example, a liquid crystal element) for forming an optical image with video signals supplied from outside, and a projector lens.
A small discharge lamp which is denoted by a metalhalide lamp or an ultra high pressure mercury vapor lamp is widely utilized as a light source for a projection display apparatus and the like. In such a case, it is general to combine the discharge lamp with a concave reflector to compose a light source apparatus and utilize this apparatus as a light source for the projection display apparatus.
FIG. 17 exemplifies a configuration of a conventional discharge lamp. A discharge lamp 321 is configured mainly by a light emitting bulb 301, sealing members 302 and 303, metal foils 304 and 305, electrodes 306 and 307, external conductors 308 and 309, and discharge media 310, 311 and 312. Quartz glass is used as the light emitting bulb 301 and sealing members 302, 303, tungsten is used as the electrodes 306 and 307, molybdenum foils are used as the metal foils 304 and 305, and molybdenum is used as the external conductors 308 and 309. Furthermore, mercury, a light emitting metals such as a metalhalide or the like, and a rare gas such as argon or the like, are used mainly as the discharge media 310, 311 and 312, respectively.
When a predetermined voltage is applied across the external conductors 308 and 309, arc discharge takes place between the electrodes 306 and 307, whereby the mercury 310 and the metal halide 311 emit rays characteristic thereof. The argon gas 312 is used to improve a starting characteristic.
Since a distance is extremely short between the electrodes and a high current is supplied at a start time in this kind of discharge lamp, the lamp is liable to be blackened due to deformation of the electrodes and evaporation of an electrode substance, and can hardly have a long service life. In contrast, there have been disclosed various kinds of lamps which are configured to have service lives prolonged by contriving structures of electrodes (for example by JPA 7-192688 and JPA 10-92377). FIGS. 18 through 20 are enlarged views exemplifying configurations of the electrodes.
FIG. 18 shows an example wherein a coil 331 is disposed around a tip of an electrode 330 to enhance a heat dissipation property, thereby preventing a tip portion from being deteriorated or deformed due to excessive temperature rise.
FIG. 19 shows an example wherein a discharge portion 342 which has a diameter larger than that of an electrode shaft 341 is formed at a tip of an electrode 340 to enhance a thermal conductivity, thereby preventing a tip portion from being deteriorated or deformed due to excessive temperature rise. This kind of electrode is used as an anode of a DC type discharge lamp.
FIG. 20 shows an example wherein a discharge member 352 having a diameter larger than that of an electrode shaft 351 is formed by winding a coil thick around a tip of an electrode 350 and fusing a tip portion so as to form a lump integral with an electrode shaft 351, and a heat dissipating member 353 is formed after the discharge member 352 by integrally fusing a coil, thereby preventing the electrode from being deteriorated or deformed. The heat dissipating member 353 is configured by a coil or a cylindrical electrode member.
However, the electrodes which have configurations shown in FIGS. 18 through 20 pose problems which are described below.
In case of the configuration shown in FIG. 18, a contact area between the electrode 330 and the coil 331 is narrow, whereby the electrode has a low thermal conductivity and cannot exhibit a sufficient heat dissipating effect. Furthermore, the electrode poses a problem that the coil 331 is fused and deformed when the coil 331 is too thin. Though this problem can be solved by thickening the coil 331, tungsten which is used as a material of the electrode 330 is hard and the coil 331 can hardly be wound when it is thick. Furthermore, the electrode poses another problem that a spot of arc discharge moves to the tip of the electrode or an end of the coil, whereby an arc is hardly be stable.
In case of the configuration shown in FIG. 19, the discharge member 342 which is too thick makes the electrode 340 hardly be heated to a temperature required to emit thermoelectrons, thereby posing a problem of degradation of a starting property and interception of discharge. This is remarkably problematic when a lamp is to be lit with an alternating current in particular, whereby the electrode can hardly be used for lighting a lamp with an alternating current.
In case of the configuration shown in FIG. 20 wherein the discharge member 352 is formed integrally and continuously with the coil 353, the discharge portion 352 and the coil 353 have high thermal conductivities and are hardly be raised to a temperature required to emit thermoelectrons, thereby degrading a starting property or allows discharge to be intercepted in the course like the structure shown in FIG. 19. This poses a serious problem when a discharge lamp is to be ignited with an alternating current in particular. Furthermore, an electrode such as that shown in FIG. 20 is manufactured by allowing the electrode having the coil 353 wound around the electrode shaft 351 to discharge in an atmosphere of an inert gas such as nitrogen gas or argon so as to fuse the tip portion. A doping agent such as thorium is often added to tungsten as electrode material for a discharge lamp to improve a starting property. However, the electrode manufactured by the method described above poses a problem that the doping material is evaporated at a stage to fuse the tip portion. Furthermore, the electrode poses another problem that the fusing promotes recrystallization of the tip portion, whereby the electrode is low in its strength and can hardly be worked.
When this kind of discharge lamp is to be used in a projection display apparatus, on the other hand, it is general to configure a light source by combining the discharge lamp with a concave reflector. FIG. 21a exemplifies a configuration of a light source. FIG. 21b is a sectional view taken along an Axe2x80x94A line in FIG. 21a. A reflective coating 372 which is formed on an inside surface of a concave reflector 371 reflects rays emitted from a lamp 360 in a predetermined direction with a high efficiency. A lamp insertion port 373 and a conductor outlet port 374 are formed in the concave reflector 371. The lamp 360 is fixed to the concave reflector 371 with a heat-resistant adhesive agent 375 after inserting a sealing member 362 is inserted into the lamp insertion port 373. Furthermore, an end of an extension conductor 376 is connected to an external conductor 369 and the other end of the extension conductor 376 is led out of the concave reflector 371 through the conductor outlet port 374. Rays can be emitted from the lamp 360 by applying a predetermined voltage across an external conductor 368 and the extension conductor 376.
It is desired that a lamp which is to be used in the projector display apparatus is as small as possible and has a long service life. However, the conventional light source shown in FIG. 21a poses problems which are described below.
First, the conventional light source poses a problem that oxidation of metal foils 364 and 365 disposed at both ends of the lamp 360 as well as the external conductors 368 and 369 results in wire breakage, thereby shortening a service life of the lamp. In case of the light source shown in FIG. 21a, distortion is produced by a thermal stress at a sealing stage, whereby a gap B is formed between the external conductor 369 and a sealing member 363 as illustrated in FIG. 21b showing an enlarged sectional view taken along the Axe2x80x94A line. Accordingly, the external conductor 369 and an end of the metal foil 365 on a side of the external conductor 369 are kept in contact with air, whereby oxidation of these parts is accelerated in an extremely high temperature condition while the lamp stays lit. When molybdenum is used as the metal foils, for example, the oxidation results in wire breakage in a time of about 5000 hours in air heated to 350xc2x0 C. though the time is variable dependently on a temperature. The external conductor 368 and the sealing member 362 are also oxidized in the similar manner.
While the discharge lamp used in the projection display apparatus stays lit, the lamp is generally kept at an extremely high temperature and heats a light emitting bulb 361 to a temperature close to 1000xc2x0 C. at maximum. Accordingly, temperatures reach hundreds of degrees in the vicinities of connected portions between the metal foils 364, 365 and the external conductors 368, 369 due to heat conduction from the light emitting bulb 361 as well as electrodes 366 and 367. Though the temperatures can be lowered by forcible air cooling with a fan or the like, evaporation of the light emitting metal is suppressed and a light emitting efficiency is remarkably lowered when the temperature of the light emitting bulb 361 is lowered. Therefore, it is therefore required to cool the lamp extremely locally with high delicacy.
In order to solve this problem, the conventional discharge lamp uses sufficiently long metal foils, thereby reducing temperature rise due to the heat conduction and preventing the wire breakage due to the oxidation. However, the conventional discharge lamp has a total length which is prolonged by the long metal foils and poses a problem that the lamp makes it difficult to configure a light source compact.
Secondly, the conventional light source poses another problem that evaporation of the light emitting metal which is evaporated while the lamp stays lit enhances an internal pressure of the light emitting bulb to an extremely high level, for example, of several MPas (mega pascals) in case of the metalhalide lamp or of scores of MPas (mega pascals) in case of the super-high pressure mercury lamp, thereby making the light emitting bulb liable to be broken while the lamp stays lit.
A primary object of the present invention is to provide a discharge lamp which is improved in a starting property, an arc stability and service life even when it uses a short arc. Another object of the present invention is to provide a light source apparatus which is suited for use mainly in a projection display apparatus, compact and highly reliable, and efficiently condense rays emitted from a discharge lamp. The light source apparatus according to the present invention makes it possible to provide a projection display apparatus which is bright, compact and highly reliable.
A first discharge lamp according to the present invention is a lamp comprising a light emitting bulb, sealing members disposed at both ends of the light emitting bulb, a pair of electrodes which are disposed in the light emitting bulb so as to oppose to each other at a predetermined spacing and a discharge medium enclosed in the light emitting bulb, wherein the electrode is configured by an electrode shaft and a discharge member which is formed integrally with a tip of the electrode shaft and has an outside diameter larger than that of the electrode shaft, and has a heat dissipating conductor which is disposed at the rear of the discharge member so as to surround the electrode shaft.
A second discharge lamp according to the present invention is a lamp comprising a light emitting bulb, sealing members disposed at both ends of the light emitting bulb, a pair of electrodes which are sealed in the sealing members and disposed in the light emitting bulb so as to oppose to each other at a predetermined spacing and a discharge medium enclosed in the light emitting bulb, wherein the electrode is composed of an electrode shaft and a discharge member which is formed integrally with a tip of the electrode shaft and has an outside diameter larger than that of the electrode shaft, the discharge member has a taper formed on its tip, a heat dissipating conductor surrounding the electrode shaft is disposed at the rear of the discharge member and the electrode satisfies the following conditions:
xcfx86/Lxe2x89xa60.6
20xc2x0xe2x89xa6xcex8xe2x89xa660xc2x0
where the reference symbol L denotes the spacing between the electrodes disposed in the light emitting bulb, the reference symbol xcfx86 denotes a diameter of the tip of the discharge member, and the reference symbol xcex8 denotes an angle formed between the tapered tip and the electrode shaft.
A third discharge lamp according to the present invention is a lamp comprising a light emitting bulb, sealing members which are disposed at both ends of the light emitting bulb, a pair of electrodes which are sealed in the sealing members and disposed in the light emitting bulb so as to oppose to each other at a predetermined spacing and a discharge medium enclosed in the light emitting bulb, wherein the electrode is composed of an electrode shaft and a cylindrical conductor fitted over a tip of the electrode shaft, and a heat dissipating conductor is disposed at the rear of the cylindrical conductor so as to surround the electrode shaft.
A fourth discharge lamp according to the present invention is a lamp comprising a light emitting bulb, sealing members which are disposed at both ends of the light emitting bulb, a pair of electrodes which are sealed in the sealing members and disposed in the light emitting bulb so as to oppose to each other at a predetermined spacing and a discharge medium enclosed in the light emitting bulb, wherein the electrode has an electrode shaft, a cylindrical conductor which is fitted over a tip of the electrode shaft and has a tapered outside diametrical portion on a side of the tip of the electrode shaft, a heat dissipating conductor surrounding the electrode shaft is disposed at the rear of the cylindrical conductor and the electrode satisfies the following conditions:
xcfx86/Lxe2x89xa60.6
20xc2x0xe2x89xa6xcex8xe2x89xa660xc2x0
where the reference symbol L denotes the spacing between the electrodes disposed in the light emitting bulb, the reference symbol xcfx86 denotes an outside diameter which is closer to the tip of the electrode shaft in the cylindrical conductor, and the reference symbol xcex8 denotes an angle formed between the tapered tip and the electrode shaft.
A fifth discharge lamp according to the present invention is a lamp comprising a light emitting bulb, sealing members disposed at both ends of the light emitting bulb, a pair of electrodes which are sealed in the sealing members and disposed in the light emitting bulb so as to oppose to each other at a predetermined spacing, and mercury and a rare gas which are enclosed in the light emitting bulb, wherein the mercury is enclosed in an amount of 150 mg/cc or more, and the electrode is composed of an electrode shaft and a discharge member which is formed integrally with a tip of the electrode shaft and has an outside diameter larger than that of the electrode shaft, the discharge member has a tapered tip, a heat dissipating conductor surrounding the electrode shaft is disposed at the rear of the discharge member, and the electrode satisfies the following conditions:
xcfx86/Lxe2x89xa60.6
20xc2x0xe2x89xa6xcex8xe2x89xa660xc2x0
where the reference symbol L denotes the spacing between the electrodes, the reference symbol xcfx86 denotes a diameter of the tip of the discharge member, and the reference symbol xcex8 denotes an angle formed between the tapered tip and the electrode, and wherein the discharge lamp is configured to be lit by applying an AV voltage across the electrodes.
It is preferable for the third or fourth discharge lamp described above that a taper is formed on an inside end which is far from the tip of the electrode shaft.
It is preferable for any of the first through fifth discharge lamps described above that the heat dissipating conductor has a form of a coil.
It is preferable for any of the first through fifth discharge lamps described above that the electrodes and the heat dissipating conductor are made of different materials.
It is preferable for any of the first through fifth discharge lamps described above that the electrodes are made of tungsten doped with thorium.
Furthermore, it is preferable for any of the first, second or fifth discharge lamps described above that the spacing between the electrodes does not exceed 2 mm and that the electrode satisfies the following conditions:
2.0xe2x89xa6D2/D1xe2x89xa65.0
D3/D1xe2x89xa69.0
where the reference symbol D1 denotes an outside diameter of the electrode shaft, the reference symbol D2 denotes an outside diameter of the discharge member, and the reference symbol D3 denotes a length of the discharge member as measured in a direction of the electrode shaft.
It is preferable for the third or fourth discharge lamp described above that the spacing between the electrode does not exceed 2 mm and that the electrode satisfies the following conditions:
2.0xe2x89xa6D2/D1xe2x89xa65.0
D3/D1xe2x89xa69.0
where the reference symbol D1 denotes an outside diameter of the electrode shaft, the reference symbol D2 denotes an outside diameter of the cylindrical conductor, and the reference symbol D3 denotes a length of the cylindrical conductor as measured in a direction of the electrode shaft.
It is preferable for any of the first through fourth discharge lamps described above that the discharge medium is mercury and a rare gas.
It is preferable for any of the first through fourth discharge lamps described above that the lamp is lit by applying an AC voltage across the electrodes.
It is preferable for any of the first through fourth discharge lamps described above that the lamp is lit by applying a DC voltage across the electrodes and that a polarity of the voltage is reversed, depending on a drive time and a number of ignitions.
It is preferable for any of the first through fifth discharge lamps described above that the electrode is made of pure tungsten having a content of at least one of potassium, silicon and aluminium which does not exceed 10 ppm.
The present invention is capable of providing a discharge lamp which is excellent in a starting property and has a long service life even if it uses a short arc.
A first light source apparatus according to the present invention comprises any of the first through fifth discharge lamps described above and a concave reflector which reflects rays emitted from the discharge lamp in predetermined directions.
A second light source apparatus according to the present invention comprises the second, fourth or fifth discharge lamp described above and a concave reflector which reflects rays emitted from the discharge lamp in predetermined directions, and is characterized in that the concave reflector has an opening through which reflected rays are emitted and a lamp insert portion which is disposed on a side opposite to the opening, that the discharge lamp is disposed so that its one end is inserted into the lamp insert portion and a center of a light emitting area formed between the electrodes is approximately coincident with a shorter focal point of the concave reflector and that rays which are emitted from the center of the light emitting area and incident onto an effective reflecting surface of the concave reflector are not intercepted by the electrodes of the discharge lamps.
A third light source apparatus according to the present invention is an apparatus comprising a discharge lamp and a concave reflector which reflects rays emitted from the discharge lamp in predetermined directions, wherein the discharge lamp comprises metal foils which are sealed in sealing members disposed at both ends of a light emitting bulb and different in lengths, the concave reflector has an opening through which reflected rays are emitted and a lamp insert hole disposed on a side opposite to the opening, and the discharge lamp is disposed so that a sealing member in which a metal foil having a shorter length is sealed is inserted into the lamp insert hole and a center of a light emitting area formed in the light emitting bulb is approximately coincident with a shorter focal point of the concave reflector.
A fourth light source apparatus according to the present invention is an apparatus comprising a discharge lamp, a concave reflector which reflects rays emitted from the discharge lamp in predetermined directions and light transmittal enclosing means which is disposed in an opening for emitting rays reflected by the concave reflector to form a enclosed space in the concave reflector, wherein an inert gas is enclosed in the closed space.
A fifth light source apparatus according to the present invention is an apparatus comprising a discharge lamp, a concave reflector which reflects rays emitted from the discharge lamp in predetermined directions and light transmittal enclosing means which is disposed in an opening for emitting rays reflected by the concave reflector to form an enclosed space in the concave reflector, wherein a gas is enclosed in the enclosed space at a pressure higher than an atmospheric pressure and lower than a working pressure of the discharge lamp.
A sixth light source apparatus according to the present invention is an apparatus comprising a discharge lamp having a working pressure not lower than 10 MPas (mega pascals) a concave reflector which reflects rays emitted from the discharge lamp in predetermined directions and transmittal enclosing means, wherein the discharge lamp has metal foils which are disposed at both ends of a light emitting bulb and different in lengths, the concave reflector has an opening for emitting rays reflected by the concave reflector and a lamp insert hole disposed on a side opposite to the opening, the discharge lamp is disposed so that a sealing member in which a metal foil having a shorter length is sealed is inserted into the lamp insert hole and a center of a light emitting area formed in the light emitting bulb is approximately coincident with a shorter focal point of the concave reflector.
It is preferable for the fourth or fifth light source apparatus described above that the concave reflector is an ellipsoidal mirror.
It is preferable for the fourth or fifth light source apparatus described above that the discharge lamp has a working pressure which is not lower than 10 MPas (mega pascals).
It is preferable for the third or sixth light source apparatus described above that the concave reflector is an ellipsoidal mirror and a distance as measured from a vertex of the lamp insert portion of an ellipsoidal to an end of a longer metal foil on a side of the opening of the concave reflector does not exceed xc2xd of a length of a major axis of the ellipsoidal surface.
The present invention makes it possible to obtain a light source apparatus which is capable of effectively condensing rays emitted from a lamp. Furthermore, the present invention makes it possible to obtain a light source apparatus which is compact and highly reliable.
A projection display apparatus according to the present invention is an apparatus comprising a light source, image forming means which is illuminated with the light source and forms an optical image in correspondence to video signals and projecting means which projects an optical image formed on the image forming means to a screen, characterized in that the light source is any of the first through sixth light source apparatus described above.
The present invention makes it possible to obtain a projection display apparatus which is compact, highly reliable and bright.